TM 1-1500-204-23-4 Figure 3-9.  Inverter (4) Replacement criteria. Inverter replacement criteria are as follows: · Replace   rotary   inverters   when any    unusual    bearing    or    gear noises are detected during operation. · Replace   rotary   inverters   when commutator     bars     are     rough, scored,   pitted,   loose,   high,   or worn  to  the  depth  of  insulating mica between bars. · Replace  rotary  inverter  brushes that are cracked, broken, chipped, unevenly worn, or worn beyond maximum wearing depth slot. · Replace   static   inverters   when electrical connectors have broken pins or cracked connector inserts. · Replace    static    inverters    that have cracked cases. · Replace static inverters that fail to operate properly. NOTE Remove components from aircraft when replacing brushes. d.  Starters.  Army aircraft are started by a device called a starter.  The starter develops large amounts of mechanical energy, causing the engine to rotate. (1) Types.  The following paragraphs name various   starters   used   with   turbine   engines.      Turbine engine    starters.        Turbine    engines    use    air-turbine (pneumatic) or electric starters.  The air-turbine starter is becoming the most common type. (2) Inspection. General inspection procedures  for  starters  removed  from  the  aircraft  and starters   installed   on   the   aircraft   are   described   in   the following paragraphs. 3-15